Electrosurgical devices are used in many surgical operations. Electrosurgical devices apply electrical energy to tissue in order to treat tissue. An electrosurgical device may comprise an instrument having a distally-mounted end effector comprising one or more electrodes. The end effector can be positioned against tissue such that electrical current is introduced into the tissue. Electrosurgical devices can be configured for bipolar operation. During bipolar operation, current is introduced into and returned from the tissue by active and return electrodes, respectively, of the end effector. Bipolar devices may also have an end effector consisting of two or more jaws each having at least one of the active and or return electrodes. At least one of the jaws is moveable from a position spaced apart from the opposing jaw for receiving tissues to a position in which the space between the jaws is less than that of the first position. Movement of the moveable jaw compresses the tissue held between. Heat generated by the current flow through the tissue in combination with the compression achieved by the jaw movement may form hemostatic seals within the tissue and/or between tissues and thus may be particularly useful for sealing blood vessels, for example. The end effector of an electrosurgical device sometimes also comprises a cutting member that is movable relative to the tissue and the electrodes to transect the tissue.
Electrical energy applied by an electrosurgical device can be transmitted to the instrument by a generator. The electrical energy may be in the form of radio frequency (“RF”) energy. The electrical energy may be in the form of radio frequency (“RF”) energy that may be in a frequency range described in EN 60601-2-2:2009+A11:2011, Definition 201.3.218—HIGH FREQUENCY. For example, the frequency in monopolar RF applications are typically restricted to less than 5 MHz. However, in bipolar RF applications, the frequency can be almost anything. Frequencies above 200 kHz can be typically used for MONOPOLAR applications in order to avoid the unwanted stimulation of nerves and muscles which would result from the use of low frequency current. Lower frequencies may be used for BIPOLAR techniques if the RISK ANALYSIS shows the possibility of neuromuscular stimulation has been mitigated to an acceptable level. Normally, frequencies above 5 MHz are not used in order to minimize the problems associated with HIGH FREQUENCY LEAKAGE CURRENTS. However, higher frequencies may be used in the case of BIPOLAR techniques. It is generally recognized that 10 mA is the lower threshold of thermal effects on tissue.
During its operation, an electrosurgical device can transmit RF energy through tissue compressed between the two or more jaws. Such RF energy may cause ionic agitation in the tissue, in effect producing resistive heating, and thereby increasing the temperature of the tissue. Increased temperature of the tissue may lead to tissue cauterization. In some surgical procedures, RF energy may be useful for removing, shrinking, or sculpting soft tissue while simultaneously sealing blood vessels. RF energy may work particularly well on connective tissue, which is primarily comprised of collagen and shrinks when contacted by heat. Because a sharp boundary may be created between the affected tissue and the surrounding tissue, surgeons can operate with a high level of precision and control, without sacrificing un-targeted adjacent tissue.